Lithium ion rechargeable batteries have several important advantages over traditional lead-acid or nickel-cadmium batteries including a higher energy density as well as, being environmentally safe. There are thus numerous consumer markets for a lithium ion rechargeable battery with a reasonable cycle life, retention of capacity and competitive manufacturing cost. Some examples of consumer markets that employ lithium rechargeable batteries include, but are not limited to: cellular phones, lap-top computers, camcorders and the like.
One important factor in the development of such rechargeable batteries is the need to find a cathode material that exhibits high capacity and high energy while being electrochemically reversible. To date, a number of intercalation compounds have been successfully developed and investigated for this purpose. Recently, an article authored by Koksbang, et al. entitled "Review: Cathode Materials for Lithium Rocking Chair Batteries", Solid State Ionics 84, 1 (1996) reviewed the properties, preparation procedures and electrochemical performance of different intercalation cathode materials for use in rechargeable lithium rocking chair batteries.
Intercalation cathode compounds such as lithium cobalt oxide (Li.sub.x CoO.sub.2), lithium nickel oxide (Li.sub.x NiO.sub.2), lithium manganese oxides (spinel phase Li.sub.x Mn.sub.2 O.sub.4) and several vanadium oxides, e.g. Li.sub.x V.sub.2 O.sub.5, Li.sub.x V.sub.3 O.sub.8 and Li.sub.x V.sub.6 O.sub.13, are known and are among the most studied of the intercalation compounds. Rechargeable lithium batteries based on the aforesaid intercalation compounds are typically cycled between 2.0 and 4.0 V vs. Li with specific capacities in the range of from about 100 to 120 mAh/g. Despite this, the nickel-, manganese- and vanadium-based intercalation compounds of the prior art suffer a significant loss of capacity with extensive cycling; see, for example, G. Pistoia, et al., "Direct Comparison of Cathode Materials of Interest for Secondary High-Rate Lithium Cells", Electrochimica Acta 37, 63 (1992) and B. Scrosati, "Insertion Compounds for Lithium Rocking Chair Batteries" in The Electrochemistry of Novel Materials, eds. J. Libkowski and P. N. Ross (VCH Publishers Inc., New York, 1994.
This loss of capacity has been attributed to a number of different factors including irreversible structural changes in the host cathode material accompanying the charge/discharge process. For a complete discussion in regard to this phenomena see, for example, M. M. Thackeray, et al., "Spinel Electrodes from the Li-Mn-O System for Rechargeable Lithium Battery Applications," J. Electrochem. Soc. 139, 363 (1992); and K. West, et al. "Vanadium Oxides as Host Materials for Lithium and Sodium Intercalation," in G. Z. Nazri, D. W. Shriver, R. A. Huggins and M. Balanski (eds) Solids State Ionics II, Materials Research Society, Pittsburgh, 1991 pp. 449-60. Much research endeavor has been thus spent on improving the reversibility while maintaining or even increasing the electrochemical capacity of intercalation cathode materials. To date, none of the prior art intercalation materials exhibit all of these properties.
In addition to developing new intercalation cathode materials, attention has been directed to improving the anode material of such lithium rechargeable batteries. For example, numerous carbonaceous materials have been investigated for use as the anode of such batteries. It has been observed that the electrochemical behavior of the carbon anode depends not only on the type of carbon materials, but also on the solvent of the electrolyte system used in lithium batteries. For instance, well-crystallized graphite, which appears to be the most attractive carbon anode because of its high capacity (one mole Li per six moles of carbon) and low electrode potential (0.01-0.2 V vs. Li), undergoes different Li-intercalation processes in ethylene carbonate (EC)/propylene carbonate (PC) and EC/dimethyl carbonate (DMC)-based electrolyte solutions. For a complete discussion regarding the electrolyte solvent dependency on graphite anodes see, for example, M. Morita, et al., J. Electrochem. Soc. 143, L26 (1996). Moreover, D. Aurbach, et al., J. Electrochem. Soc. 141, 603 (1994) has reported that graphite shows negligible reversibility but large irreversible capacity when PC or tetrahydrofuran (THF) were used as the solvent of the electrolyte solution. The irreversible capacity loss of the graphite anode has been attributed to the reduction of PC or THF on the graphite surface during the first Li-intercalation process.
Despite the current state of the art, there is still a need to develop new and improved intercalation cathodes and/or anodes which do not suffer from any of the disadvantages mentioned with prior art intercalation electrodes. That is, there is a need to develop intercalation cathodes and/or anodes that are highly reversible yet maintain or increase their electrochemical capacity without altering the structure of the electrode host material. Moreover, it is desirable to provide a cathode and/or anode that contains a host material that has large, but open channels of mesoscale dimension since the same would result in a material that has high electrochemical capacity and enhanced ionic transport. Such properties can not be afforded with prior art materials such as amorphous, crystalline or spinel-type metal oxides or with prior art carbonaceous materials.